[mythtv-users] Recording directly to RAID

Tapani Tarvainen mythtv at tapanitarvainen.fi
Fri Jul 27 20:15:35 UTC 2012

On Jul 27 13:27, David Engel (david at istwok.net) wrote:

> Is anyone recording directly to RAID?  If so, what type/size, how many
> simultaneous recordings and how well does it work?

I've got a 5-disk RAID10 array in a fileserver used by
mythtv over NFS in addition to one local disk.
It can handle 10 simultaneous recordings without blinking.
(Or at least could once when I tested it - besides that I don't
think I've ever had more than five.)

And the disks aren't particularly fast either: 2TB Seagate Green
5900 rpm disks. But in the RAID10 setup they can pull rather
impressive speeds, writing over 300MB/s and reading 600MB/s
for single stream, and what's more, multiple simultaneous
processes get almost the same in aggregate.
Key there was using offset (o2) layout with biggish (4M) block size -
defaults are rather ridiculous.

Enough RAM and good SATA controller are also important.
(I like LSI HBA cards.)

> The two configurations I'm primarily considering are either a 4-disk
> RAID6 array or a pair of 2-disk RAID1 mirrors.  While the RAID6
> configuration should be more reliable, in theory, I'm leaning toward
> the RAID1 configuration.  One big reason, and the reason for this
> email, is the increased seek load on all drives with RAID6 when 4 or
> more recordings are in-progress.

With four disks I'd go for RAID10 without question.

Tapani Tarvainen

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